The present invention relates to a radiowave monitoring method and apparatus which can identify a location of a radiowave emitting source, such as an illegal radio station or the like usage, in a prescribed area and monitor radiowave environments.
Conventionally, in identifying a location of a radiowave emitting source, such as an illegal radio station in a prescribed area, monitor stations are disposed at a plurality of positions, and the respective radiowave monitor stations observe arrival bearings of the radiowaves from the radiowave emitting source by means of Yagi-Uda array antennas, goniometers or others. The respective monitor stations plot the arrival bearings on a map to thereby estimate the location of the radiowave emitting source, based on an intersection of the respective bearings.
The above-described conventional method is based on the presumption that radiowaves from a radiowave emitting source being monitored propagate rectilinearly along a single path to a monitor station. Actually, however, radiowaves from a radiowave emitting source propagated to a monitor station, in some cases are diffracted by or reflected on topographies, and ground objects, such as buildings, etc. Radiowaves from a radiowave emitting source propagated to a monitor station, in other cases, are separated in multi-paths under the influence of topographies and ground objects. The estimation of a location of a radiowave emitting source by the conventional method noted above has a problem that radiowaves are diffracted or reflected or divided into multi-paths, which lowers accuracy of estimating the location of the radiowave emitting source.
The inventors of the present application already proposed a wide-area radiowave monitoring method and apparatus which can solve the above-described problem (refer to, e.g., Japanese Patent Application Laid-Open Publication No. Hei 11-326482 (1999)).
In the wide-area radiowave monitoring method described in Japanese Patent Application Laid-Open Publication No. Hei 11-326482 (1999), through a computer simulation, one or more monitor stations are disposed in a certain area, radiowave emitting sources are assumed to be present at a plurality of locations in the area, and arrival bearings of radiowaves from the radiowave emitting sources that propagate to the monitor stations are computed for the respective radiowave emitting sources, incorporating the topographical information of the area, while the monitor stations observe, for respective divided propagation paths, radiowaves from a radiowave emitting source. The arrival bearings observed by the monitor stations, and the results of the computer simulation are compared with each other to detect the computer simulation results for arrival bearings of the results, which are most similar to the observed arrival bearings of the radiowaves, and a corresponding location is judged to be a potential location of the radiowave emitting source. Further, on the presumption that the radiowave emitting source is present near the potential location, the computer simulation is executed, while djusting a location of the radiowave emitting source, to thereby determine the final location of the radiowave emitting source.
The above-described method can accurately determine a location of a radiowave emitting source even in a case that radiowaves are diffracted or reflected.
However, in the wide-area radiowave monitoring method and apparatus described in the specification of Japanese Patent Application Laid-Open Publication No. Hei 11-326482 (1999), arrival bearings of radiowaves incoming to the monitor stations from radiowave emitting sources at a plurality of locations in an area are computed by the computer simulation for the respective locations, which requires a plurality of sets of data base provided by the computer simulation of the radiowave propagation to be prepared for unidentified radiowave emitting sources. Furthermore, it takes much time to prepare the data base.